1. Field of the Invention
The present invention relates to an organic electroluminescence device.
2. Background of the Related Art
With the recent trend of a display device's growing in size, the need for a flat display device occupying a small space is increasing. As one of such flat display devices, the technology of organic electroluminescence device, known as an organic light emitting diode (OLED), has been developed rapidly, and a variety of sample products have been already released.
An organic electroluminescence device includes an organic film which is formed between an electron injecting electrode(cathode) and a hole injecting electrode(anode), and emits light generated upon extinction after electrons and holes are paired. The device can be formed on a flexible transparent substrate, such as plastic, can be driven at a lower voltage (below 10V) than a plasma display panel or inorganic electroluminescence(EL) display is, has relatively low power consumption, and has a superior color sense. Further, the organic electroluminescence(EL) device can represent three colors of green, blue and red, and thus is drawing a great deal of attention as a next-generation full-color display device.
Here, the procedure of fabricating an organic electroluminescence device will be described briefly.
(1) Firstly, an anode material is coated on a transparent substrate. Indium tin oxide(ITO) is often used as the anode material.
(2) A hole injecting layer(HIL) is coated thereon. Copper phthalocyanine(CuPC)is mainly used as the hole injecting layer at a thickness of 10 to 30 nm.
(3) Then, a hole transport layer(HTL) is coated. 4.4′-bis[N-(1-naphthyl)-N-phentylamino]-biphenyl(NPB) is deposited and coated at 30 to 60 nm as the hole transport layer.
(4) An organic emitting layer is formed thereon. At this moment, a dopant is added thereto as needed. In case of green luminescence, tris(8-hydroxy-quinolate)aluminum(Alq3) is deposited at a thickness of 30 to 60 nm as the organic emitting layer, and MQD(N-methyl quinacridone) is commonly used as the dopant.
(5) An electron transport layer(ETL) or electron injecting layer(EIL) are consecutively coated thereon, or an electron injecting transport layer is formed thereon. In case of green luminescence, Alq3 of the above (4) has a good electron transport capability, and thus it is often the case that no electron injecting/transport layer is used.
(6) Next, a cathode is coated, and finally a protecting layer is coated.
In the above structure, blue, green and red light emitting devices each can be realized depending on how a light emitting layer is formed.
The organic electroluminescence device forms excitons by the combination of holes from the hole transport layer and electrons from the electron transport layer. At this time, the excitons are protons that conduct heat without being accompanied by the movement of an electric charge in a semiconductor or insulating body.
The excitons thus generated are dispersed a relatively long distance before extinction, and thus increases the possibility of some parts of the excitons being dispersed out of the light emitting layer. In some cases, the excitons are dispersed and quenched by the anode. To reduce this phenomenon, a hole blocking layer is used which can disperse electrons, substantially support the dispersion of excitons, and substantially prevent the dispersion of holes.
However, the hole blocking layer according to the prior art is low in stability, and thus is unable to prevent the quenching of the excitons to a satisfying level.